Monitoring of plasma and milk progesterone for evaluation of postpartum estrous cycles and early pregnancy in mares.

This research paper explores the use of progesterone levels in plasma and milk to track the reproductive cycle and early pregnancy of mares. The findings suggest that tracking progesterone levels in plasma or milk can provide an accurate picture of a mare’s estrous cycle, which can inform breeding programs.

Study Methodology

• This study focused on 13 mares, measuring their plasma and milk progesterone levels three times weekly for a period of five months, starting from the point of parturition (giving birth).
• The research distinguished between two phases of a mare’s estrous cycle: estrus and diestrus. Estrus was identified by a progesterone concentration of less than 1 ng/ml, and diestrus was identified when progesterone levels were equal to or greater than 1 ng/ml.

Results and Findings

• Based on the aforementioned differentiation, the research found an average estrus period of 8.9 days, a diestrus average of 13.9 days, constituting an overall estrous cycle average of 22.8 days.
• Progesterone concentration during estrus averaged 0.4 ng/ml in plasma and 2.2 ng/ml in milk. For the diestrus phase, the corresponding values were 6.8 and 6.9 ng/ml respectively.
• In early stages of pregnancy, the average progesterone concentration measured 5.4 ng/ml for plasma and 4.7 ng/ml for milk.
• The research found a similar pattern of progesterone in both milk and blood plasma, with a correlation of 0.7 between 362 paired values (p<0.01).

Research Conclusions and Implications

• Based on the above results, the researchers concluded that a mare’s estrous cycle can be accurately mapped by measuring progesterone content in plasma or milk at regular intervals of two to three days.
• This findings of this research were also used to propose a breeding program monitored by blood progesterone levels, which could serve as an effective tool in equine reproduction management.